Cutoff-frequency phase-in ILC to overcome initial position offsets

The previous works to deal with initial position offset in iterative learning control are in time domain. This article proposes a frequency domain method to deal with this problem. In the proposed method, the cutoff frequency of the filter phases in along a predefined profile from a high value to a low value on the time axis. The high cutoff frequency at the beginning part of cycle can effectively suppress the influence of initial state error on learning. Experimental results show that this method can handle initial position offsets.